The objective of the TCR core is to provide the Project leaders access to TCR spectratyping technology, single stranded conformational polymorphism (SSCP) analysis, subcloning, sequencing and screening of ap-TCR repertoires, and acquisition of TCR repertoire analytical databases. Projects 1, 2 and 3 will be heavily reliant on the identification of T cell clones specific to vaccinia, yellow fever, influenza A and Epstein- Barr viruses among healthy, diseased, or vaccinated individuals over the 5 year study period. The essential aspects of each proposed study are to define the distributions of virus-specific cells among TCR Va- and Vp- families and to analyze the structural nature and evolution of the TCR a- and p-chains. Each Project leader will initiate the technical procedures in his/her own laboratory and give them to the TCR core for further treatments and analyses. The demonstrated expertise of the Core Director in TCR repertoire analyses will ensure a high quality of TCR analyses throughout the Program Project.